1. Field of the Invention
The present invention relates to a brine temperature control apparatus, for controlling brine within a wide temperature range, and more specifically concerns a brine temperature control apparatus using a three-way proportional valve in the brine circulating fluid path.
2. Description of the Related Art
Formerly, when the temperature of brine which is supplied to a load is to be controlled inside a temperature range of xe2x88x9230xc2x0 C. to +80xc2x0 C., driving of a cooling unit (also referred to as a xe2x80x9cchillerxe2x80x9d) is first halted and then applied heat is supplied to the brine from a heater.
FIG. 3 illustrates an example of a known type of brine temperature control apparatus, in which a cooling unit 1 is constructed by a compressor 4, a condenser 5, an expansion valve 6 and a heat exchanger 7 connected together successively in series. In the case that the temperature of the brine is controlled over a wider temperature range, the cooling unit may be made up of an array of plural units.
On the other hand, the circulating circuit 2 is constructed by a brine tank 11, a pump 12 and a load 13 connected successively in series, wherein the heat exchanger 7 and a heater 14 are disposed inside the tank 11. Driving and halting of the cooling unit 1, along with supply of electricity to the heater 14, are controlled by a temperature controller 16, which is operated in accordance with a temperature sensor which detects the brine temperature in the tank 11.
In this known type of temperature control apparatus, for example, when the temperature of the brine is controlled at +80xc2x0 C., a control is performed in which only one cooling unit 1 is operated as a cooling source, and heat is also applied from the heater 14 to the brine in the tank 11, that has been cooled by the cooling unit 1.
Further, when the temperature of the brine is controlled at +30xc2x0 C., a control is performed in which two cooling units 1, 1 are operated as the cooling source (such an arrangement of two cooling units is not actually shown in FIG. 3 although such a structure is easily understood), while heat is applied by the heater 14. When the brine temperature is to be controlled at xe2x88x9230xc2x0 C., a control is performed in which multiple cooling units 1 are operated simultaneously. In all of these examples, after the brine has been cooled in excess of the received heat from the load 13, heat must be applied from the heater 14.
As described above, when controlling brine temperature according to this known type of temperature control apparatus, a plurality of cooling units 1 may be operated for controlling brine temperature, however, there is a limit to the precision of the temperature control by operating and halting of the cooling units 1. For raising precision, after cooling in excess of a predetermined temperature, it is necessary to apply heat using the heater 14, so there is a problem of a large wasting of energy.
In order to address such a problem, according to Japanese Utility Model Disclosure Document No. 5-17535, a temperature control apparatus has been proposed in which it is possible to control temperature over a wider temperature range with higher precision, and moreover, in which energy consumption is lower. Such an apparatus, as shown in FIG. 4, is characterized by a refrigeration circuit and cooling liquid circulating circuit, wherein the cooling liquid circulating passage further comprises an auxiliary coolant path 78 which branches from an outlet side of the pump 74, and then passes through an ON/OFF type of electromagnetic valve 79 and the heat-exchanger 61, providing fluid transport in a recirculating manner back to the tank 62. Further, the temperature controller 76 causes the ON/OFF type electromagnetic valve 79 to open when the temperature of the cooling liquid in the tank 72 is higher than a preset temperature, and causes electricity to be supplied to the heater 73 when the cooling liquid temperature falls below a preset temperature.
The basic operation of the this known type of apparatus may be described as follows, with reference to FIG. 5. When the temperature of the cooling liquid in the tank 72 is higher than, for example 0.4xc2x0 C. above, a preset temperature, the ON/OFF electromagnetic valve 79 is opened by the temperature controller 76, so that the cooling liquid which flows through the auxiliary coolant flow path 78 is chilled by the heat exchanger and quickly recirculates back to the tank 72. In the case that the cooling liquid temperature becomes lower than the preset temperature set in the temperature controller 76, for example 0.1xc2x0 C. below the preset temperature, the ON/OFF electromagnetic valve 79 is closed. In addition when the temperature falls about 0.4xc2x0 C. below the preset temperature, heat is applied from the heater 73, until the temperature rises to about 0.35xc2x0 C. below the preset temperature, at which point the heater 73 is turned off. Thus, by combined operations of the electromagnetic valve 79 and the heater 73, the temperature of the cooling liquid in the tank 72 can be maintained inside the preset temperature range of the temperature controller 76.
Because cooling of the cooling liquid in the auxiliary coolant path 78, as well as application of heat by the heater 73, is selectively performed by raising and lowering the cooling liquid temperature with respect to the preset temperature range, compared to the case of applying heat by a heater to a previously-cooled cooling liquid for controlling to a set temperature range, consumption of energy can be lessened overall, while notwithstanding, the temperature control is highly accurate. Further, by selectively cooling and applying heat to the cooling liquid, control over a wider temperature range is made possible.
However, the apparatus according to Japanese Utility Model Disclosure Document No. 5-17535 has experienced problems of its own. In particular, this apparatus uses an electromagnetic ON/OFF type valve 79 and a heater 73, making up an ON/OFF system, which enables temperature control over a wide range from about xe2x88x9220xc2x0 C. to +90xc2x0 C. However, because of use of the ON/OFF type of electromagnetic valve 79, during abrupt ON/OFF switching operations of the electromagnetic valve, an undesirable xe2x80x9cwater hammerxe2x80x9d effect has been generated. The problem is all the more aggravated in the case of large capacity chiller units, resulting in a cumbersome and vexing disadvantage which has yet to be fully solved. Because of the water hammer effect, it has not been possible to implement this system in large capacity chiller units.
The present invention is a brine temperature control apparatus in which the temperature of brine in a tank disposed in a brine fluid circulating passage is controlled using a three-way proportional valve. Because the three-way proportional valve does not open and close in an abrupt ON/OFF fashion, but rather the degree of opening on the side for supplying chilled brine is gradually adjusted in proportion to a detection signal indicative of the brine temperature in the tank, a water hammer problem is avoided, and therefore a coolant circulating circuit including such a three-way proportional valve can be used effectively even with large capacity cooling units.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.